Glass tempering is a process by which glass is thermally treated to increase its strength. During tempering the glass is subjected to high heat until its softening point is reached and then the glass is rapidly cooled. This creates a tension zone in the interior of the glass, which is surrounded by a compression zone. These zones contribute to high stress within tempered glass. Glass generally needs to be cut or ground to a desired geometry before tempering, because, once tempered, the glass cannot be cut or it will suffer catastrophic breakage into small pieces due to the high stress imparted in the glass during tempering.
Conventionally, electronic devices, such as electrochromic devices, are fabricated on tempered glass. The desired size of glass is chosen; the glass is tempered and only then is the electronic device fabricated thereon. Thus, if a device is fabricated on a glass substrate and then the glass substrate is tempered, the device would be exposed to the tempering process. Conventionally, this process destroys functionality of the device.